Your grandmother's friend will be named as such in the will.  See if she will provide you with a copy.  If not, you can obtain a one from the probate court where the will was filed;  this would be in the county where your grandmother resided at the time of her death.  Also, if you are a beneficiary the court will notify you as well.  Typically, in most states a will must be presented to the court within 30-60 of the testator's death.  However, this does vary.  To be sure of Michigan state law you should consult with an attorney in the area or contact the applicable probate court.

If you contact the probate court in the county she either resided in or where she passed away, they will give you further information on obtaining a copy from the court file, if they have recieved it.  If a court file has not been opened, and your grandmother's friend will not give you a copy or is acting suspicious, you should contact me, John R. Tatone, to discuss your options.  586-868-5100 ext. 17